A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces. When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read-write head that is positioned over a specific location of a disk by an actuator. A read-write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. Write heads make use of the electricity flowing through a coil, which produces a magnetic field. Electrical pulses are sent to the write head, with different patterns of positive and negative currents. The current in the coil of the write head induces a magnetic field across the gap between the head and the magnetic disk, which in turn magnetizes a small area on the recording medium.
With perpendicular magnetic recording (PMR) based HDDs, a typical PMR head includes a trailing write pole, a trailing return pole or opposing pole magnetically coupled to the write pole, and an electrically conductive magnetizing coil surrounding the write pole. The bottom of the return/opposing pole has a surface area greatly exceeding the surface area of the tip of the write pole. Write current is passed through the write coil to create magnetic flux within the write pole. The magnetic flux passes from the write pole tip, through the hard magnetic recording track on the media, into the soft under-layer in the magnetic media, and across to the return/opposing pole to complete perpendicular writing process.
Increasing areal density (a measure of the quantity of information bits that can be stored on a given area of disk surface) is one of the ever-present goals of hard disk drive design evolution. As areal density increases, the recording data rate preferably increases accordingly. For example, the recording data rate for a 3.5″ 7200 RPM desktop product may achieve greater than 2.4 Gb/s. Such a high data rate requirement on the PMR writer demands a fast writer with much reduced write field rise time for recording at high frequencies. Meanwhile, the high data rate PMR writer design also needs to meet stringent reliability requirements, such as requirements associated with Wide Area Track Erasure (WATER). The WATER reliability issue is especially important for short yoke length PMR writer configurations, which intrinsically have worse WATER margins. Therefore, a dynamically fast writer with improved off track erasure or WATER capability may be desirable.
Any approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.